Today, we ask if horseshoe nails are real. The
University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.

You've all heard the old
rhyme,

For want of a nail, the shoe was lost;
For want of the shoe, the horse was lost;
For want of the horse, the rider was lost;
For want of the rider, the battle was lost;
For want of the battle, the kingdom was lost;
And all for the want of a horseshoe
nail.

That innocent little poem contains a theory of
cause and effect. So I've been asking history
colleagues if they believe in metaphorical
horseshoe nails. They won't give me any easy
answer. Of course history teems with candidates for
real-life horseshoe nails that actually might've
redirected human affairs:

On June 4, 1942, cloud cover briefly parted,
exposing the Japanese fleet to American planes. We
gained the advantage in the Battle of Midway
Island, and the war in the Pacific turned in our
favor. What if we hadn't found that hole in the
clouds? What if lightning had killed Ben Franklin,
as it did so many people who tried to replicate his
kite experiment? What if the captain of the
Titanic had said
"I don't like the look of it. Let's slow down tonight,"
or if the launch manager of the shuttle
Challenger had said,
"You're right, it really is too cold for those O-rings."

Does history really turn upon such coincidences? We
know that any complex future is highly vulnerable to tiny influence. The
smallest change in today's weather radically
changes the weather five months later. That's why
mathematical models for the weather can predict
weather for only a few days. But, argues one
historian friend, you and I aren't weather. We're
endowed with free will.

That first struck me as a non sequitur. Then
I looked at it in the light of what I know about
nonlinear mechanics. Maybe you know the term
strange attractor. That's a pattern of
behavior which any complex system more or less
replicates in the long term. It's out of the
question to predict the weather at a given hour,
one year hence. No technology ever will. But we can
predict trends. We know roughly when to expect
hurricanes or drought.

Perhaps that's how history works. If one rider's
lost, another takes his place. Maybe the will of
the people forms a sort of strange attractor that
brings us out in the same place, despite horseshoe
nails. Go back to that one bad decision you made,
long ago -- the one that ruined your life.
Actually, it's just the one decision you remember
most acutely. Your life is, in fact, the sum of a
million decisions, mostly forgotten. Your life
might well have closed back in upon the pattern
built of all those other decisions.

So I don't know what role horseshoe nails play in
the larger tapestry of history. And, in the end,
it's not really a question for historians. It is,
rather, a matter for mathematicians and
philosophers. And not even they will keep me from
acting as though I have control over who and what I
am.

I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.

(Theme music)

I'm grateful to colleagues Sarah Fishman-Boyd, Joseph
Glatthaar, and Richard Blackett from the University
of Houston History Departmant. Their lunchtime
conversations were most helpful to me in thinking
this issue through. The subject first arose when
Glatthaar, a noted Civil War historian, told us that
Confederate troops at Gettysburg carried artillery
ammunition from a new armory. The delay on the fuses
was slower than normal, and their shells exploded
five hundred yards beyond the Union troops. Was that
a turning point in the battle, I wondered? (Probably
not, for exactly the reasons I cite above.)